Wednesday, February 10, 2010

Pitot-booms

Formula One's meagrely rationed series of pre-season tests resumed at Jerez on Wednesday this week, and, as scheduled, Red Bull took the opportunity to unveil their much-anticipated RB6. In fact, the RB6 superficially resembles the RB5, even down to the extent of possessing the same pull-rod rear suspension featured on the 2009 vehicle. In contrast, every other team this year has opted for push-rod rear suspension.

Push-rod suspension places the rockers and spring-dampers up top, and therefore potentially compromises the dorsal airflow between the rear wheels, over the beam wing, and over the top of the diffuser. In contrast, pull-rod suspension places the rockers down low, thereby potentially compromising the volumetric capacity of a double-diffuser. By opting for the latter solution, one presumes that Red Bull designer Adrian Newey has discovered that the greatest net effect comes from maximising the airflow over the top of a moderately-sized double diffuser.

McLaren have opted for a huge double-diffuser on the MP4-25, and turned up at Jerez with an interesting Meccano-like device behind the left-side front-wheel. At first sight, this lateral boom appeared to be a mechanism for spraying rivals with DDT. Closer inspection, however, suggested it was equipped with pitot-static tubes, to measure airspeed and static air pressure.

Of particular interest was just how far out this contraption projected. The airflow in this region is both crucial and complex. The front wing of the car, and the rotating front wheel, both generate a turbulent wake, and these wakes interact with each other in a complex manner, albeit a manner which can be heavily influenced by the design of front-wing endplate. The interaction between these wakes partially determines the dorsal airflow between the rear wheels, and thence partially determines the performance of the diffuser. Getting this part of the airflow correct is therefore paramount, hence McLaren's use of their pitot-boom.

Whether the use of such a diagnostic tool indicates that McLaren have problems again, is another matter...